## Why
Users can stop one meeting and immediately start the next while the previous meeting is still draining transcription, speaker recognition, or summarization. Per-run buffers and artifacts must remain isolated so old transcription output cannot be written to the new meeting.

## What Changes
- Keep meeting note, transcript session, artifact paths, and run options bound to the run that created them.
- Allow a new recording to start after the previous capture has stopped even while the previous run continues final processing.
- Ensure rapidly-created artifact filenames are distinct.

## Impact
- Recording coordinator finalization paths use immutable per-run state instead of mutable current-run fields.
- Transcript, meeting note, assistant context, and summary filenames include higher-resolution timestamps.